1. Field of the Invention
This invention relates to systems for converting solar energy into electrical energy, and more particularly to such systems which incorporate a load requiring a high initial starting current.
2. Discussion of Related Art
The use of solar energy as a power source is becoming increasingly more popular, especially in areas that have a relatively constant level of high intensity solar radiation available. One very popular use of solar energy is in producing domestic hot water for heating swimming pools and other uses. Such systems utilize a heat exchange liquid, such as water, which is circulated between a storage tank and a solar collector panel by use of a pump which is normally started and stopped in response to the level of insolation. It is also known to isolate the pump electrical supply from municipal power supply grids by using photovoltaics in order to eliminate the fear of a reduction in efficiency by parasitic power consumption. One example of a circulation pump operated by photovoltaics is disclosed in U.S. Pat. No. 4,147,157 to Zakhariya.
While the use of photovoltaics to operate a domestic hot water circulation pump is attractive from the point of view that the sun controls the systems operation without reliance on an outside electrical source, serious drawbacks of such systems do exist. If the photovoltaic panel is installed with the same orientation as the thermal collector, the panel may take up to 90 minutes to produce a sufficient charge to start the circulation pump. On the other hand, in the evening, the photovoltaic panel may cause the circulation pump to operate too long.
One solution to the problem of late circulation is to orient the photovoltaic array 20.degree. to the east relative to the thermal collector. However, an oversized photovoltaic panel must be used resulting in a higher cost. Furthermore, some systems using larger photovoltaic panels are still plagued with late starts and stops.
Many electrical power supplies have been suggested using solar energy. None of these known systems solves the two problems mentioned above, namely, providing enough current from a photovoltaic panel to start a circulation pump during the morning hours, and controlling the amount of current passed to a circulation pump so that the pump will not operate when insolation is reduced below an effective limit.
U.S. Pat. No. 4,100,427 to Durand et al. shows a device for converting solar energy into electrical energy. In the Durand et al system, a plurality of electric accumulators in the form of batteries are connected to a plurality of photocells. A switching means is provided for connecting a load to the photocells only so that load current is determined by the photocell current during the starting period of the load.
U.S. Pat. No. 4,122,396 to Grazier et al. shows a stable solar power source which includes a capacitive means having a large capacitance connected in parallel with a plurality of interconnected solar cells in order to offset fluctuations in currents applied by the solar cells.
U.S. Pat. No. 2,889,490 to Paradise shows a solar powered light source which produces visible flashes of light in the daytime or nighttime. The system includes an elementary relaxation oscillator comprising a resistor, a capacitor and an inert gas-filled flash tube. The relaxation oscillator is fed from a parallel combination of a solar cell and a battery. During daylight hours, the battery is charged from the solar cell and, at night, the solar cell becomes inoperative.
U.S. Pat. No. 3,317,809 to Bowers et al. shows a self-contained electrical lighting unit which includes a first bank of solar cells connected to recharge a battery, and a second bank of solar cells which actuates a relay. The relay is operative to complete a circuit connecting the battery to the first bank of solar cells or connecting the battery to a light.
U.S. Pat. No. 3,980,996 to Greenspan et al. shows a self-sustaining alarm transmitter device which includes a storage element connected to energize an output transmitting circuit on the occurrence of an alarm condition to maintain the storage element at full charge. A trickle charging circuit is provided which includes an energy conversion device for converting solar energy, broadcase electromagnetic energy, heat energy or the like into an electrical current suitable for charging the storage element.